Scroll machinery for fluid compression or expansion is typically comprised of two upstanding interfitting involute spirodal wraps or scrolls which are generated about respective axes. Each respective scroll is mounted upon an end plate and has a tip disposed in contact or near contact with the end plate of the other respective scroll. Each scroll further has flank surfaces which adjoin, in moving line contact or near contact, the flank surfaces of the other respective scroll to form a plurality of moving chambers. Depending upon the relative orbital motion of the scrolls, the chambers move from the radially exterior ends of the scrolls to the radially interior ends of the scroll for fluid compression, or from the radially interior ends of the scrolls to the radially exterior ends of the scrolls for fluid expansion. The scrolls, to accomplish the formation of the chambers, are put in relative orbital motion by a drive mechanism. Either one of the scrolls may orbit or both may rotate eccentrically with respect to one another.
A typical scroll machine, according to the design which has a non-orbiting scroll, includes an orbiting scroll which meshes with the non-orbiting scroll, a thrust bearing to take the axial loads on the orbiting scroll, and a lubricant supply system for lubricating the various moving components of the machine including the thrust bearing.
The typical lubricant supply system incorporates a lubricant sump in the lower or bottom portion of the housing into which the drive shaft extends so as to pump lubricant therefrom to the various portions of the compressor requiring lubrication. In addition, the lubricant also often acts to aid in the removal of heat from the various components of the compressor. In order to insure that sufficient lubricating oil is contained within the sump to assure adequate lubrication and/or cooling of the moving parts while also minimizing the overall height of the housing, it is sometimes necessary that the lubricant level within the housing extend above the rotating lower end of the rotor. The higher viscosity of the lubricant as compared to refrigerant gas can create an increased drag on rotation of the portion of the rotor submersed in lubricant, thus resulting in increased power consumption. This problem can be further aggravated in scroll-type compressors which employ a counterweight secured to the lower end of the rotor and thus also submersed in the lubricant.
U.S. Pat. No. 4,895,496 discloses a cup-shaped shield member which projects above the oil level in the sump and is positioned in surrounding relationship to the lower end of the rotor via a close fit with the drive shaft whereby the oil level in the area within the shield is reduced by the initial rotation of the rotor upon startup and return oil flow into this area is greatly restricted. Thus, the oil induced drag on the rotor and the resulting increased power consumption of the motor is greatly reduced. In one embodiment, a rotation inhibiting projection is provided on the shield while in another embodiment the shield is allowed to rotate with the drive shaft although the speed of rotation thereof will be substantially less than that of the drive shaft due to the drag exerted thereon by the lubricant. In both embodiments, however, the power consumption of the motor is greatly reduced thus resulting in significant improvement in the operating efficiency of the compressor.
While the above described shield does reduce motor power consumption by substantially eliminating the viscous drag of the lubricant on the rotor, it also eliminates or significantly reduces the amount of lubricant being circulated across the lower end turns of the stator. In some applications, it may be desirable to achieve the advantages of this higher operating efficiency while also maintaining a substantial flow of lubricant across the stator end turns for cooling of same.
U.S. Pat. No. 5,064,356 discloses a shield which is carried by the drive shaft and allowed to freely rotate therewith. This shield incorporates a generally flat circular disk or flange positioned in close proximity to the lower end of the rotor which serves to restrict return flow of oil to the area of the rotating rotor and/or counterweight but still enables some circulation of oil across the adjacent stator end turns. This increase in lubricant circulation results in improved cooling of the stator end turns without any substantial effect on the overall operating efficiency of the compressor.
While the above described shield in the U.S. Pat. No. 5,064,356 does allow for the increase in circulation of oil across the adjacent stator end turns, this approach, similar to the approach taken in the U.S. Pat. No. 4,895,496 completely isolates the lower counterweight from the oil sump. The lower counterweight due to its rotation within the compressor has a large pumping capacity. This pumping capacity could be utilized to improve the oil circulation in the area surrounding the motor stator to improve motor cooling.
The present invention provides an oil circulation system which does not isolate the lower counterweight but restricts the oil circulation around the lower end of the motor stator in such a way that it controls the oil circulation's net effect on motor cooling as well as power loss versus the oil level within the lubrication sump.
Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings.